The trophoblastic invasion of maternal vessels results many changes in extracellular matrix, which gives rise to high uteroplacental vessel distensibility to accommodate the increased blood flow. So, İn normal pregnancy, there is a wide spread vasodilatation, with increased arterial compliance and reduced peripheral vascular resistance.In preeclampsia, however, trophoblastic invasion is reduced, leading to incomplete modification of maternal spiral arteries and therefore to decreases in placental perfusion.